Bioluminescence provides a useful read out for the detection of reactions in a background of optically complex materials such as cells and tissues and the signal-to-noise ratio can be very high.
Luciferases are enzymes that generate visible light through the oxidation of a specific substrate in the presence of oxygen and usually a source of energy (such as Mg2+ and ATP). The reaction between firefly luciferase and the substrate luciferin, yields oxyluciferin, carbon dioxide and visible light with a maximum around 560 nm and with other wavelengths of light output identifiable by a skilled person.
For these reasons, bioluminescence and in particular luciferin and related compounds are routinely used for in vivo imaging applications and for additional techniques for in vitro and/or in vivo detection of targets and/or reactions.